The reduction of semiconductor device dimensions is increasing the density of semiconductor circuitry to a point where interconnect line-to-line capacitance is impacting the speed (due to propagation delay) and reliability (due to crosstalk noise) of semiconductor devices. Manufacturers are addressing this is by incorporating changes to semiconductor device fabrication processes. One change includes conversion of the interlayer dielectric (ILD) from silicon dioxide-based (SiO2-based) materials (e.g. conventional SiO2, which has a dielectric constant of approximately 3.9-4.2 and fluorinated silicon dioxide, which has a dielectric constant of approximately 3.5) to lower dielectric constant (low-k) materials. Decreasing the dielectric constant of the ILD decreases line-to-line capacitance and its associated effects.
Carbon-doped oxides (CDOs) are one class of materials being investigated to replace SiO2-based ILDs. CDOs typically have lower dielectric constants than SiO2-based materials (i.e. some can have dielectric constants of 2.0 and below). However, other properties can make their integration problematic. For example, the modulus of elasticity (i.e., mechanical strength) of CDOs is significantly lower than that of SiO2-based materials. Chemically vapor deposited (CVD) SiO2 has a modulus of elasticity of approximately 60-70 gigapascals (GPa). Carbon-doped oxides on the other hand, typically have a modulus of elasticity less than 15 GPa. Low modulus of elasticity materials are more susceptible to deformation and damage when subject to compressive, tensile, and sheer stresses. The inability to withstand stresses during, for example, chemical mechanical planarization, die singulation, wafer probe, wire bond, die attach, etc., limits the attractiveness of CDOs because in addition to the CDO process itself, expensive and time consuming process/retooling changes must also be made at other processing stages to accommodate the presence of the CDO.
Another class of materials being considered for use as an ILD includes that of zeolites. Zeolites are highly ordered porous structures that typically have pore diameters less than approximately two nanometers. Because of their ordered nature, they are mechanically stronger than carbon-doped oxides. And, because of their porous nature, they can have lower dielectric constants than that of conventional SiO2-based materials. The use of pure silica zeolites as an ILD material is known. For example, U.S. Pat. No. 6,630,696 to Yan describes an insulation material comprising a pure silica zeolite (i.e., silicalite). Pure silica zeolites are reported to have a modulus of elasticity of 30-40 gigapascals (GPa), an experimentally demonstrated dielectric constant as low as 1.8, and a theoretical dielectric constant of approximately 1.6.
It will be appreciated that for simplicity and clarity of illustration, elements in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Where considered appropriate, reference numerals have been repeated among the drawings to indicate corresponding or analogous elements.